I've used the cork sides and rubber half circle pieces.
The little tabs on the ends of the rubber help fill the gap between the oil pan and the cork gaskets, shouldn't have to trim anything.
I do use a generous amount of silicone on those corners, otherwise I despise silicone gasket stuff.
Use some contact adhesive to stick the gaskets to the oil pan, and Permatex #2 for pan gasket to block.

I bet everyone has a different method, this is what's worked for me.

Grigg

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
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"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-